Rule One
Each row uses 1–9 once
Every horizontal row must contain all nine numbers with no duplicates.
The rules are simple. The puzzle is not always so polite.
How to Play Sudoku
Sudoku is a logic puzzle played on a 9-by-9 grid. Your goal is to fill every empty square with a number from 1 through 9 without repeating a number in any row, column, or 3-by-3 box.
Rule Two
Each column uses 1–9 once
Every vertical column follows the same rule: one of each number, no repeats.
Rule Three
Each box uses 1–9 once
Each outlined 3-by-3 box must also contain every number from 1 through 9.
Getting Started
Look for what is missing
Some numbers are already placed when the puzzle begins. These are your clues and cannot be changed. Start with a row, column, or box that is nearly complete, then ask which number is missing.
Before placing a number, check all three areas connected to that square: its row, its column, and its 3-by-3 box. A number is valid only when it does not already appear in any of them.
831
6?9
274
The missing number is 5.
Helpful Techniques
A few ways to get unstuck
Scan rows, columns, and boxes
Move across the board looking for areas with only one or two empty squares. They usually offer the easiest starting points.
Use candidate notes
When more than one number could fit, write the possibilities in the square. Remove candidates as other numbers are placed nearby.
Find the only possible square
Sometimes a number can appear in only one square within a row, column, or box—even when that square has several candidates.
Do not guess
A standard Sudoku can be solved with logic. When you feel stuck, revisit your notes and scan from a different direction instead of tossing in a chaos number.
Take your time
Sudoku is not a math test. The numbers are symbols, and no arithmetic is required. Settle in, follow the logic, and let the grid slowly surrender.